Eleven-year-old Ella Koehler, of Seattle United soccer club, heads the ball at a practice on the University of Washington campus. It's the first year she and her teammates of the same age can use the technique. A 2015 rule by the U.S. Soccer Federation banned heading for kids ages 10 years old and younger.
Robert Monges, a coach for James Lick High School, checks tight end Dominic Brewster for a concussion during a football game played in Morgan Hill, Calif., in 2006.
Patrick Tehan/San Jose Mercury News/MCT/Landov